1. Field of Invention
The present invention relates to a method of fabricating an integrated circuit (IC). More particularly, the present invention relates to a method of fabricating a barrier applied in contact/via plugs.
2. Description of Related Art
To match the ever increasing complexity and precision requirements of semiconductor integrated circuits, two or more metal interconnect layers formed above a substrate are common in semiconductor manufacturing. At present, a contact plug is used for connecting one terminal of a MOS component with a metallic layer, and a via plug is used for interconnecting two different metallic layers. One of the plugging techniques now employed by most VLSI circuit manufacturers is the tungsten plug.
Sandwiching another material between two layers in contact (such as tungsten and silicon) can prevent the intermixing of materials from these two layers. The role of this third material is to prevent the diffusion of the two materials into each other, or to resist the tendency of a chemical reaction to form a new phase between the adjoining materials.
Titanium nitride (TiN) is an attractive material as a contact/via barrier in silicon ICs because it behaves as an impermeable barrier to silicon, and because the activation energy for the diffusion of other impurities is high. Titanium nitride is also chemical and thermodynamically very stable.
Usually, titanium nitride films do not make direct contact to silicon; instead, a contact/via structure consisting of metal/TiN/Ti/Si is widely adopted. Such contact/via structure exhibits low resistivity and remarkably high thermal stability, with the ability to withstand temperatures up to 550xc2x0 C. without failures.
In a conventional process for fabricating a barrier with a TiN/Ti/Si structure, a thin titanium layer is formed by sputtering and a titanium nitride layer is deposited over the titanium layer by reactive sputtering deposition. However, if the titanium nitride barrier formed by the conventional method is applied in a high aspect ratio contact, the thickness of the titanium nitride layer in the bottom of the contact window is usually insufficient.
Accordingly, the present invention is directed to providing a method of forming a barrier layer in contact/via plugs, which can reduce RC delays of the plugs, thereby enhancing the performances and the reliability of the plugs.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention includes a method of forming a barrier layer in contact/via plugs. Particularly, the method of the present invention is suitable for forming a titanium/titanium nitride barrier layer within an opening with an aspect ratio higher than 5, preferably higher than 7.
As embodied and broadly described herein, the invention provides a method for forming a titanium/titanium nitride barrier layer, comprising: providing a substrate having an interlayer with an opening; forming a titanium layer conformal to a profile of the opening and over the substrate by an ion metal plasma process; performing a first gas-stable step for adjusting pressure by supplying a hydrogen gas, a helium gas, a reactive source and a carrier gas; depositing a first titanium nitride layer on the titanium layer by using metal organic chemical vapor deposition (MOCVD) with the reactive source and the carrier gas after performing the first gas-stable step; performing a first plasma treatment process to remove a portion of the first titanium nitride layer; performing a second gas-stable step for adjusting pressure by supplying the hydrogen gas, the helium gas, the reactive source and the carrier gas; depositing a second titanium nitride layer on the remained first titanium nitride layer by using MOCVD with the reactive source and the carrier gas after performing the second gas-stable step; and performing a second plasma treatment process to remove a portion of the second titanium nitride layer.
The opening within the interlayer can be a contact opening or a via opening. The reactive source and the carrier gas used in MOCVD are tetrakis(dimethyl)amino titanium and helium, respectively. Both the first and the second plasma treatment processes use a nitrogen/hydrogen plasma to treat the first and the second titanium nitride layers.
The average value of RC delays by using hydrogen gas in the gas-stable step is lower than that of using nitrogen gas in the gas-stable step by about 13%, while the average value of reflection indexes by using hydrogen gas in the gas-stable step is lower than that of using nitrogen gas in the gas-stable step by about 14%. By using hydrogen gas in the gas-stable step before depositing the titanium nitride layer, the RC delay and reflection index of the resultant barrier layer are substantially reduced, thus increasing the performance of the contact/via plug.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.